Scottish Shellfish Farm Production Survey 2023

Spat settlement

Following anecdotal shellfish farming sector reports of poor spat settlement and mortality in 2010, Marine Directorate developed a questionnaire which was sent to all authorised aquaculture production businesses farming common mussel. This 2011 investigation indicated that poor spat settlement and mortality were not widespread in Scottish waters, although they had major impacts on certain individual producers. As a result of talks between the Association of Scottish Shellfish Growers and the Marine Directorate, a spat collection question was introduced to the 2013 survey. This question focused on common mussel spat collection and was presented in two parts: is this a spat collection site; if yes, was spat settlement sufficient for production purposes?

Responses were received from 233 (100%) of the sites authorised for common mussel production in 2023. Ninety-five (41%) of these were spat collection sites, 54 (57%) of which reported that they had sufficient spat settlement for production purposes. Insufficient spat settlement on sites may require movement of common mussel to that site which increases the risk of introduction or spread of diseases.

Chart 11 Common mussel spat settlement.

Chart shows trends in number of spat collection sites on mussel farms (turquoise dashed line) and whether the amount of spat collected is sufficient for farm requirements (solid blue line).

Data Source: Scottish Shellfish Farm Production Survey 2023, Supplementary Tables, Table 5.